This invention relates to an apparatus for on line inspection of an intermediate-stage product, namely headed, nonthreaded blanks for subsequently threaded fasteners. The blanks are produced in a continuous stream by a cold forming machine, and production of blanks is stopped when the inspecting apparatus detects a flaw in the output of the cold forming machine.
In the production of headed, threaded fasteners, it has long been known to feed selected wire stock to a machine that automatically severs a blank segment, from a supply of wirestock, and cold forms the severed segment into a headed intermediate blank. Rolling machines later cold form threads into the blank stem of the headed intermediate product. A typical headed intermediate blank provides an axially elongated stem that extends from one end of a fastener's head which is of enlarged diameter relative to that of the stem. Both the stem and head are cold-formed.
One form of intermediate product provides a head section which includes a hex head that terminates in a integral washer. The free end of the hex head is provided with a hex-shaped, axially elongated, drive socket, and the integral washer is of greater diameter than either the head or the unthreaded stem. The term "drive socket", or "recess", when used herein refers to a shaped indentation in the head section of a fastener that is intended for use with a driver for the fastener, and is to be distinguished from a mere indentation in a fastener's head that merely exists to save some weight of the material used to form the fastener. The washer is located at the junction between the hex head and the stem, or shank. Other typical intermediate blanks for fastener members provide, in the enlarged head at one end of the blank stem, a "Phillips"-shaped, drive socket, adapted to receive therein a "Phillips"-head driver, or a "Pozi"-drive socket, or other drive sockets such as a "Torx" socket and other sockets that are known in the trade and are adapted to receive driving tools thereinto. The "Torx" drive system not only refers to a recessed hex-lobed socket but also to a hex-lobed axial projection.
Such blanks, when their respective stems, or work-entering ends are threaded, become fasteners and may be used in vast quantities in certain industries, such as the automotive industry. It is desirable, and may even be critical, that all recessed head drive systems, that are adapted to receive therein a drive, such as the hex-socketed, "Phillips", "Pozi", slotted, "Torx", and other such fasteners should be made to conform to exacting specifications in order for the automated equipment that install the fasteners to function satisfactorily. It is therefore important that the intermediate blanks be accurately formed.
The cold forming of metal parts by automatic machines has been known for many years, and the problems associated with avoiding production of defective parts has been known for the same length of time. In the manufacture of intermediate blanks by automatic machines that cold form wire stock segments into the finished blank, it has been found that the cold-forming tool that is most likely to fail is the one that makes and shapes the blank's head. Variations in specified maximum dimensions of the head end of the blank are one result of such failure that may require rejection of a blank, or of the resulting fastener. Other defects are lack of concentricity of head and blank stem, and incorrect depth of the end recess, or drive socket, of hex-socketed, "Phillips"-headed, "Pozi"-drive, and other like fasteners. It is estimated that a large majority of all failures in production of machine screw fasteners occur in the portions of the fastener's blank other than in its stem. Problems in the formation of the stem, itself, will usually be reflected in the head of the fastener. It has also been observed that the process of cutting segments from the supply of wire stock, to provide the blank segment which is then cold-formed into the intermediate headed blank, is extremely reliable. A critical phase in threaded fastener manufacture is, therefore, in the cold-forming of the intermediate blank.
A first known type of in-process control device utilizes as the principal, significant, control-parameter a force-time signal, that is, a measurement of force applied at the time of fastener blank formation. The force is measured by a sensor which generates signals, that are fed to an electronic processor which is programmed to recognize signals that reflect distortions in the fastener formation, and to initiate machine shut-off. Such a system and instrument is called "Processor-SE" and has been offered for sale in the United States by Brankamp Process Automation, Inc. of Lexington, Mass.
A second approach to the same problem uses, as input, information as to load levels developed in the machine that is forming the headed blank stem parts. By using load-sensing transducers and comparing changes in the force levels in the metal working tooling, through and with an electronic comparator, the system is able to determine if the producing machine should be shut down. Such a system is known by the trademark "PARTGARD", which is offered in the United States by Helm Instrument Co., Inc. of Toledo, Ohio.
Still another approach to the problem has been to provide multiple separate monitors to monitor forces generated in the cold-forming machine, to monitor the part-forming punch in order to detect any significant wearing or breaking and to monitor the output blanks to detect variations in the length of the blank stem. Such a system is known as "Auto-checker", offered by Yarisute of Osaka, Japan and available in the United States through the Shinsho American Corp. of Lake Bluff, Ill.
It is generally believed that failures in formation of fasteners will, with very high probability, be determined by examination of multiple features at the head of the blank. Determination of variation in stem length are often eschewed because length variations of a cold-formed blank product, formed from a substantially fixed volume blank segment, are likely to result in measurable dimensional, and/or geometrical variations in the blank's head, or in the axial alignment of the blank's head with the stem's axis.
A system known under the name "HEADSTART", and offered by HI-TEC SEIKO, of Japan, provides alternate systems, each dedicated to the testing of only a single headed blank, especially one of the kind that has been recessed during cold-forming to provide a blank for either a hex washer head screw, or a Phillips head screw. The "HEADSTART" system feeds a sample blank through and along a vertical slot bounded by a pair of support rails, for supporting the blank's head, and spaced a fixed distance apart and arranged to discharge the forwardmost blank into an elongated, U-shaped, recess provided in the edge of a rotatable table. The table then rotates to move the sample headed blank to a test station. A gauging apparatus at the test station is lowered to engage and to rotate the blank and to provide entry of a gauge into the recess in the blank's head. A spring loaded, crank arm lever feeler, is positioned to engage the outer surface of the rotating blank. The lever feeler measures eccentricity of the axis of the blank's head relative to the axis of the blank's stem, or in the case of hex washer head blanks, the feeler measures corner build up adjacent the washer. The "HEADSTART" system, because of its dedication to testing only multiple duplicates of a single part, fails to provide flexibility for testing runs of blanks of different sizes, and therefore is considered to be inadequate for usage in a factory facility that may use a single production machine that can, when desired, be modified to produce runs of different sized fastener blanks.
T. Hamatani, in U.S. Pat. No. 3,878,726 discloses a structure for advancing a selected sample of a batch of coldformed headed cross-holed screws to a testing apparatus. The testing apparatus measures the depth of engagement of a cross-pointed gauge shaft with the cross hole, referred to as a Q value, of each screw of the sample. In the form of measurement disclosed, electrostatic capacity between a rotary drum attached to the gauge shaft and a fixed electrode is measured to determine the amplitude of motion of the gauge shaft.
Watkin, et al. in U.S. Pat. No. 3,435,685 had earlier disclosed the broad concept of an apparatus for sampling and measuring physical parameters of discrete objects by selectively withdrawing a sample from a stream of discrete objects and measuring that sample. Hamatani uses the same general concept disclosed in said earlier patent to Watkin et al., but provides a different apparatus for making measurements on the sample.
The first two systems described above use complex electronic systems to make measurements that are related to the operation of the machine in the formation of the blank, rather than by checking the actual blank itself. The third system primarily checks features that are related to the operation of the machine, but it also measures a single dimensional variable in the output blank, namely the length of the wire cut off, to determine whether production by the machine is satisfactory. In the "HEADSTART" and Hamatani systems, the machine will not catch a defect in the blank that involves unusual distortion, such as a laterally enlarged washer, or a washer that is too small, or a hex-head of unusually reduced height above the washer. Also, these systems use machines that are dedicated to only one specific product, and hence lack versatility.
Systems that rely upon monitoring of the cold-forming machine, rather than by monitoring the dimensions of the blanks themselves, rely upon the inference that the product is accurately formed if the forming machine operates, within predetermined tolerances, in a predetermined manner. It is believed, however, that checking the headed blank is more reliable, and ultimately less expensive, than checking the operation of the machine that produces the product.